Stabilization of 1,1,1-trichloroethane



United States Patent 3,452,107 STABILIZATION 0F 1,1,1-TRICHLOROETHANEWesley L. Archer, Midland, and Elbert L. Simpson, Au-

burn, Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Filed Dec. 1, 1967, Ser. No. 687,131Int. Cl. C07c 17/42 US. Cl. 260-6525 2 Claims ABSTRACT OF THE DISCLOSUREThe reaction of 1,1,1-trichloroethane with aluminum is inhibited by thepresence in the 1,1,1-trichloroethane of a small amount of a dissolvednitrogen heterocyclic substituted trimethylamine. Concentrations of theorder of 0.0-1 gram mole per liter provide significant inhibition.

Background of the invention This invention relates to the stabilizationof chlorinated solvents. More particularly, the present inventionconcerns the stabilization of 1,1,1-trichloroethane in the presence ofmetallic aluminum.

Chlorinated hydrocarbons such as trichloroethylene and perchloroethyleneare commonly used as solvents in chemical processes, dry cleaning, andmetal degreasing. Solvents of this type are subject to slowdecomposition and oxidation reactions, particularly in the presence ofimpurities such as water, traces of acid or metal salts. Corrosion ofmetal surfaces in containers and process equipment and deterioration ofsolvent quality by formation of acidic and colored byproducts therebybecome serious problems. Inhibitors such as acid scavengers andantioxidants are commonly added to these solvents in order to preventsuch degradative reactions. Inhibitor concentrations are normally of theorder of one percent by weight or less.

1,1,1-trichloroethane poses a different and a particularly difiicultstabilization problem because of its unusual reactivity with certainmetals, notably aluminum. Traces of metal salts, moisture, or otherimpurities are not needed to initiate the 1,1,1-trichloroethane-aluminumreaction, for this reaction occurs spontaneously on a freshly exposedaluminum surface with spectacular results, converting the solvent andthe metal surface in a few minutes to a blackened mass of acidic,carbonaceous material and aluminum salts. Conventional acid acceptorstabilizers cannot be depended upon to inhibit thealuminum-l,1,1-trichloroethane reaction and suitable inhibitors must bediscovered by independent investigation. The search has yielded feweffective compounds and these show little or no obvious pattern ofstructure. Typical 1,1,1-trichloroethane formulations contain about fivepercent by weight of inhibitor which is usually a combination ofcompounds to inhibit reaction of the solvent with a variety of metals.

Summary of the invention It has now been found that the1,1,1-trichloroethanealuminum reaction can be substantially retarded orprevented by incorporating into the 1,1,1-trichloroethane an inhibitingamount of a heterocyclic substituted trimethylamine of the formula CH3 AoH,-N

CH3 wherein A is a nitrogen heterocyclic radical of the group 3,452,107Patented June 24, 1969 l-aziridinylmethyl and 2-pyrrolyl, their formulasbeing respectively;

l l /NOHgand N CH7 H These compounds may be used alone or in combinationwith each other.

Detailed description Only a quantity of heterocyclic amine compoundsutlicient to retard or to stop the reaction of aluminum and1,1,1-trichloroethane need be used. Although any significant amount willprovide some inhibition, preferably about 0.01-1 gram mole per liter of1,1,1-trichloroethane composition is employed and about 0.01-0.1 grammole is usually most preferred.

Compounds as defined by the general formula set forth above were testedfor inhibiting activity in elongated glass test tubes having an insidediameter of 0.8 cm. and 33 cm. in length. To each vertically disposedtube there was added 0.54 g. of essentially pure l-6-32 mesh granularaluminum and a solution of the inhibitor in purified1,1,1-trichloroethane to make a total volume of test mixture of 5 ml.The closed ends of the test tubes were then immersed in an oil bath heldat a temperature sufficient to maintain the 1,1,1-trichloroethanesolution in each tube at a steady reflux. The results listed in thefollowing examples indicate the minimum concentration of the inhibitorfound effective to provide complete inhibition of the1,1,l-trichlorethane-aluminum reaction for 24 hours under theseconditions. Prevention of the reaction for this length of time under thedescribed conditions indicates capacity for effective inhibition for anindefinite period. Concentrations are given in gram moles per liter,this figure being convertible to weight percent by the equation(moles/liter) (mol. wt. of inhibitor) 13.46 For example, a concentrationof 0.10 g. mole per liter of an inhibitor of molecular weight of 134.6is equal to 1.0 weight percent of that inhibitor.

Wt. percent= Effective concenagainst reaction with aluminum by havingdissolved therein a stabilizing amount of 2-pyrrolylmethyldimethylamine.

2. The composition of claim -1 wherein the inhibitor is present in aconcentration of 0.01-1 gram mole per liter of composition.

References Cited FOREIGN PATENTS 1,144,702 3/1963 Germany.

LEON ZITVER, Primary Examiner.

MATTHEW M. JACOB, Assistant Examiner.

U.S. Cl. XtR. 252-153

